I would like to reduce the noise, basically and give them a warmer sound for summing, but I'm not sure which opamp would suit me best here and if it possible to remove some el caps aswell.
I'm half the way to recapping them and it would be a good time to mod them.
Thanks,

Define "warmer", please. I did not swap chips because I wanted to change the sonic impront of the desk. I believe that improving measurable parameters will improve sound somhow, though. That´s why I´ve replaced the TL072s with OPA2132/2134 except the Faderamp position with LT1358 for some technical reason: lower selfnoise, better drivecapability at the insert point (with EQ engaged) and LT1358 running with a better OSI as faderbuffer. It´s quite some time ago that I did it and hence cannot remember if I had to tweak the bandwidth limitation of the opamps.
I did change many other things, too. The Scorpions were made on a budget and had some corners cut. By todays standards there can a lot be improved in terms of parts quality. Not on a budget, though. So I changed the gainstructure of the desk, changed many EQ frequencies and EQ caps, increased many electrolytics, removed some electrolytics. Added many many bypass caps, additional rail buffering, most important renewed the ribbon wires and fader connectors.
When you swap opamps you always have to check if the circuit oscillates. You cannot judge from listening that it runs flawlessly. If you don´t measure you risk damaging all or some of the new chips, overheating, headroom problems, increased distortion, ..... If you don´t know how to measure oscillation let someone else do it or better leave the desk in a working state as it is.
hope that helps

Hi
It is fairly easy to tell if your 'mods' have caused unwanted oscillation because you get a little trail of smoke from your tweeters and maybe the monitor amp as well. It could appear on the headphone mixes too. Probably won't hurt the desk much though.
Matt S

Maybe under severe conditions, but most of the time the oscillations are low levels, sometimes as low as a few millivolts. You need good test gear to see them and the understanding of their cause and cure. Stray capacitance on scope probes can also cause it leading the inexperienced on to a long path of chasing ghosts.

A final check with a good distortion analyzer will tell you if things have degraded or not.

Define "warmer", please. I did not swap chips because I wanted to change the sonic impront of the desk. I believe that improving measurable parameters will improve sound somhow, though. That´s why I´ve replaced the TL072s with OPA2132/2134 except the Faderamp position with LT1358 for some technical reason: lower selfnoise, better drivecapability at the insert point (with EQ engaged) and LT1358 running with a better OSI as faderbuffer. It´s quite some time ago that I did it and hence cannot remember if I had to tweak the bandwidth limitation of the opamps.
I did change many other things, too. The Scorpions were made on a budget and had some corners cut. By todays standards there can a lot be improved in terms of parts quality. Not on a budget, though. So I changed the gainstructure of the desk, changed many EQ frequencies and EQ caps, increased many electrolytics, removed some electrolytics. Added many many bypass caps, additional rail buffering, most important renewed the ribbon wires and fader connectors.
When you swap opamps you always have to check if the circuit oscillates. You cannot judge from listening that it runs flawlessly. If you don´t measure you risk damaging all or some of the new chips, overheating, headroom problems, increased distortion, ..... If you don´t know how to measure oscillation let someone else do it or better leave the desk in a working state as it is.
hope that helps

Thank you.

I was planning on changing the fader opamp (U3) for a LME49720 as I did in the s1000 modules (including a pair of .1uf mono ceramic caps from 4 & 8 to ground). Were I'm not that sure is if I can remove every el cap from the power distribution to the U2 position (2nd opamp). U2 is also compromised by the fader switch as I saw in the circuit diagram (if I'm not mistaken), so I was thinking of the possibility of swaping that one too. When I said warmer I was thinking of some kind of a dirty sound as a tape saturation would do. Options; that's what I'm searching by modding the s3000 modules.

I'm not a technical guy in this matter, but I'm trying to learn as I go. Until now everything is going smoothly and clean; above all, clean. Always following tips from the guys who know better. When I fill the it's too much, I prefer playing it safe.

Well, not wasted, I have another cheaps and olds preamps with tl072 or equivalent.

This bundle (dual lme49990 on DIP) is similar that anothers I got (AD825, AD767, etc) for avoid to me to work with SOIC in DIY learning & experiments.

I find also an advantage for me, because, curiously I found this kits more cheapest that the shop prices for the individual IC's: farnell, digikey, mouser, etc.

I found a TL072 on my pre73 and want to test if replacement have audibles changes. You said: Not in the audio path !!! a mistake then, I did not find any IC in the "originals" schemas, and really replace the tl072 for anothers (opa2134, lme49720na) don't change, not audible. I am waiting to receive an scope to see.

I do not buy the first time, investigated and never told me. avoid "or large commercial stocks" NOS/OLD items and try to find really or some credible, "old man" garages sales. A measure of protection is not spending much money, just a few dollars, try harder, but then buy a few months later to have the desired amount.

I began to search 2sc3329bl in March.

Despite these precautions, I got some faulties 2sc3329bl and some Motorola 2N3055 fakes.

"hard to find" also expresses this fact.

After a few tricks, you get some reliable suppliers.

Yes! I Lost some bucks (near 15$) but after get 50 toshiba's by 5$. I think the balance is favorable.

My gear now is 20dB's noise floor better for only 25$. No expensive or esoterics mods.

Well. First day of testing and a small issue jumped up.
The S1000 modules are eating all the power from the PSU.
Both lights from the 10A of the PSU go out when I plug more than 1 strip.
Me first guess is that the mono ceramic caps from the rail to ground are eating the power of the PSU.

I could have bought the wrong mono ceramic caps for this purpose.
Her are some photos of the S1000 modules.

Mods:

AML preamp kit
Fader amp LME49720
Removed every el cap that was left on the strip leaving only the ones on the preamp section.

Hello John
Basically because I don't understand some issues and somethings on the circuit and satisfy my curiosity and learn:

Yes, that I thought.
This is not in the signal path and apparently should not affect, however I did this test and I was surprised by my curiosity:

With a 180ohm resistor and near cranck maximum gain (position 75db, output at 4pm).

With the LME49990, I have not been exhaustive testing because I'm more than a month with all my gear apart and began with acoustic treatment in my bedroom-studio.

I do not have the full test with pictures but in a quick test, observed (listening) noise spikes, but with the same noise floor than opa2134. LME49990 it seemed bit clearer, flat, but showed a strong 20dB peek distortion near 100Hz. I could not put the opamp bypass to ground before dismantle all my gear.

Only a bit: I have a ground Issue on the PSU board to solve (you can see at 50Hz with harmonics).

Hey, yeah, this thread is about another topic, but if you want I can pm you and let you know what all was done to my GAP.

Or start another thread here maybe.

Anyway, the ground thing...yeah. The chassis is floating of course on this thing, because of the line lump transformer.

Those nasty ceramic disc caps in the input and outout...yank them things.

Thing is, it then sounds better, but is oscillating for some reason when you take them out. My guess is, that in place of a real grounding scheme, and to save money using a wallwart, these are in there as a low pass filter for rfi? If you take them out, then ground the chassis it stops, and is quiet.

when I finish the acoustic treatment, in a couple of weeks, I will continue my learning-research to solve things in my pre73, collecting info, pictures, samples and data to open a new topic thread about.

Returning to the topic (excuse me):

Beware !!! with my lasts messages. LME49990 is not a direct replacement for the TL072.

- Drastic change in the sound of the board for good. REALLY open; detailed across the entire bandwidth.

- Board is really sensible now. Tracking drums with almost every pad engaged. Trying always to give the pre a stable amount of gain (about half the way through).

- Crackling pots and faders. WTF?!!?! Didn't happen before...

- Even though I was really careful with levels, I encountered distortion peaks from time to time. I couldn't get a decent level in the board without saturating the converters. There was no correlation between the meters on the board and the ones on PT. Thing that didn't happen before either.

I uploaded some more photos from the strips with details of the mod and an audio sample from the test where you can reference the sound aswell as the distortion problem.

I ****ed up somewhere!!!
Shorting the caps of the power (stupid mistake) ****ed something.
I'm mising something... C 22 ??? or the 2.2 uf cap on the overload section....
The bypass caps are not the appropriates

I'll take one of the modules back to its original state and test it. I'll post something later this week.

Hi
Maybe it is not as 'stable' as you think.
OK it doesn't oscillate when sitting still but some op amps in certain configurations can partially 'latch up' or other misdemeanors when overdriven.
The SSM2015 (mic pre chip) was good at this in that if you took it to clipping the output would give a short burst of oscillation which you had to wait to finish before it would go 'linear' again. The SSM2016 had this problem solved as I used it as a plug in replacement on the AMEK Classic.
Matt S